Technical Field
This invention relates to internal combustion engines, and more particularly to methods and system for estimating air charge into cylinders in such engines.
Background
As is known in the art, cylinder air charge estimation has been an essential part of engine controls for port fuel injection internal combustion engines (ICE). Such estimation is typically performed using signals from various engine sensors. For example, a method called xe2x80x9cmanifold fillingxe2x80x9d is described in U.S. Pat. No. 5,331,936 xe2x80x9cMethod and Apparatus for Inferring the Actual Air Charge in an Internal Combustion Engine During Transient Conditionsxe2x80x9d, inventors I. A., Messih, L. H. Buch, and M. J. Cullen, issued Jul. 26, 1994, assigned to the same assignee as the present invention. This xe2x80x9cmanifold fillingxe2x80x9d method is used to perform air charge estimation for ICE equipped with mass airflow sensors (MAF). Another method, called xe2x80x9cspeed densityxe2x80x9d, described in U.S. Pat. No. 6,115,664 xe2x80x9cMethod of Estimating Engine Chargexe2x80x9d, inventors M. J. Cullen and C. D. Suffredini, issued Sep. 5, 2000, assigned to the same assignee as the present invention, is used to perform air charge estimation for ICE equipped with manifold absolute pressure sensors (MAP). It should be noted that other sensors, for example, throttle angle sensor, inlet air charge temperature sensor, engine coolant temperature sensor, etc., may also be required.
As is also known in the art, both the MAF-based manifold filling method and the MAP-based speed density method have their respective strengths and weaknesses, see_Toc9674602 an article by entitled xe2x80x9cCylinder air-charge estimation for advanced intake valve operation in variable cam timing engines_Toc9674602xe2x80x9d by Mrdjan Jankovic and Steve W. Magner, published in JSAE Review 22 (2001) 445 452. The main advantage of MAF is that, in steady state operation, it actually measures the cylinder: mass airflow. The challenge is, therefore, to accurately account for the intake manifold filling and emptying during transient operations such as large rapid tip-in/tip-out conditions. Compared with an MAF sensor, the main advantages of the MAP sensor are its relative proximity to the engine air intake port and lower cost. On the other hand, MAP based air charge estimation does not have as good a steady state property as compared with an MAF based air charge estimation.
For some applications, a single method such as manifold filling or speed density, may not work adequately to provide the required accuracy for air charge estimation. For example, as discussed in U.S. Pat. No. 5,398,544, xe2x80x9cMethod and system for determining cylinder air charge for variable displace internal combustion enginexe2x80x9d inventors, D. Lipinski, D. Robichaux, issued Mar. 21, 1995, assigned to the same assignee as the present invention, in a Variable Displacement Engine when operation modes change from a first number of cylinders to a different number of cylinders, the MAF based air charge estimation method may not always be able to provide accurate air charge estimation during the transient operation between such modes due to the limited bandwidth of the MAF sensor.
Several approaches have been developed in the past decade or so in order to improve the accuracy of air charge estimation. One approach is described in U.S. Pat. No. 5,889,204 xe2x80x9cDevice for determining the engine load for an internal combustion enginexe2x80x9d, inventors M. Scherer, T. Ganser, and R. Wilczek. With such approach, a Kalman-filter type estimator is used to estimate air charge. More particularly, a Kalman filter is used to estimate manifold pressures at the beginning and end of a working cycle. An air charge estimation is obtained by adding the estimated mass air flow in throttle to an amplified difference value of the two manifold pressures as calculated by the Kalman filter, with the amplification coefficient calibrated before hand. It is noted however that the Kalman filter, which is nonlinear and stochastic, is very difficult to obtain. Further, the final output may have the drawbacks of both manifold filling and speed-density approaches.
In accordance with the present invention, a method is provided for estimating cylinder air charge (CAC) in an internal combustion engine, such engine having a mass airflow (MAF) sensor and a manifold absolute pressure (MAP) sensor. The method provides such cylinder air charge estimation from signals produced primarily by the manifold absolute pressure sensor during engine transient conditions, i.e., during a change in an engine operating parameter, e.g., throttle plate position change, valve timing change, change in the number of operating cylinders in a variable displacement engine, variable cam timing change, change in lift with a variable valve lift engine. During a transition period between the transient condition and a steady-state engine condition the method combines signals primarily from both the mass airflow sensor and the manifold absolute pressure sensor to provide such cylinder air charge estimation. During the steady-state condition, the method uses primarily only the mass airflow sensor to provide such cylinder air charge estimation.
In accordance with the present invention, a method is provided for estimating cylinder air charge (CAC) in an internal combustion engine. The method provides such cylinder air charge estimation using a speed density algorithm during engine transient conditions. During the steady-state condition, the method provides such cylinder air charge estimation using a manifold filling algorithm. During a transition period between the transient condition and a steady-state engine condition the method combines the estimation from the manifold filling algorithm with the estimation from the speed density algorithm to provide such cylinder air charge estimation.
With such method, the cylinder air charge estimation method utilizes the advantages of both measurement sensors and corresponding air charge estimation algorithms. When transient situation occurs, the engine controller utilizes measurements from MAP sensors together with measurements from other less significant sensors to produce the cylinder air charge estimation. When it is determined that the transient situation is converging to a steady state operation, a smoothing algorithm is employed to combine the measurements from both MAF and MAP sensors, together with measurements from other less significant sensors, to produce the cylinder air charge estimation. Finally, when the engine is operating in steady state, only the MAF sensor, together with measurements from other less significant sensors, is used to produce the cylinder air charge estimation.
The details of one or more embodiments of the invention are set forth in the accompanying drawings and the description below. Other features, objects, and advantages of the invention will be apparent from the description and drawings, and from the claims.